When a submarine cable is to be laid in shallow waters, e.g. to provide a short haul or medium haul link, it has been conventional practice to provide heavy wire armouring to protect the cable from ships' anchors and trawls, particularly beam trawling equipment. Further, as conventional cables incorporate a high voltage power supply for repeater operation it has been necessary to provide relatively thick insulation. The cable is then relatively bulky and presents a handling problem. Even for the installation of a relative short link, it is necessary to bring a dedicated cable laying ship to the cable manufacturing installation so that the cable may be loaded into the ship. It will be appreciated that this procedure can present a severe logistics problem e.g. when the cable installation path is remote from the factory and/or when the cable ship has to be recalled from a remote location for loading the cable. This can represent a significant factor in the cost of an installation.
In recent years there have been two major developments in cable technology. The first has been an improvement in optical fibre quality which, coupled with developments in optoelectronic technology, has rendered repeaterless links feasible over short and medium haul distances, e.g. between the United Kingdom and Belgium. The second development has been in cable burying technology, whereby the cable may be laid in a ploughed trench to provide protection from the aforementioned shipping activities. It is generally considered that damage from shipping is unlikely to occur at depths greater than about 550 meters.
Various workers have addressed the problem of providing lightweight armoured cables for land use. One such construction is detailed for example in specification No. GB-A-2186098 which describes the use of tape armour for protection e.g. against rodents. However, it will be appreciated that developments in land cables cannot be readily adapted to submarine cable technology as the conditions under which the cable are installed and the environments which they must withstand are so different. For example, a submarine cable must have sufficient tensile strength to withstand the laying process and must also provide effective protection of the transmission package against hydrostatic pressure.
It is an object of the invention to provide a lightweight armoured submarine optical cable.
It is a further object of the invention to provide a submarine cable that is of reduced diameter whereby to facilitate shipping and installation.
It is a further object of the present invention to provide a submarine optical cable of the kind described having a cost-effective armouring.